With repetition: you are allowed to choose the same item more than once. For example, $ABC$ is an allowable choice of three items, and so is $AAC$.
Without repetition: you are not allowed to choose the same item more than once. For example, $ABC$ is still an allowable choice of three items, but $AAC$ is not.
Ordered: the order of items makes a difference. For example, $ABC$ and $CBA$ are different selections and are both counted. Likewise $AAC$ and $ACA$.
Unordered: the order of items makes no difference. For example, $ABC$, $ACB$, $BAC$, $BCA$, $CAB$, $CBA$ are all regarded as the same and therefore count as one possibility, not six. Likewise, $AAC$, $ACA$, $CAA$ count as one possibility, not three.
If you understand what a bit string is, I'm sure you can now work out whether repetition is allowed or not, and whether order is important or not.